In turbomachine systems, a number of original equipment manufacturers (OEMs) are replacing conventional bearing systems with magnetic bearing systems. Magnetic bearing systems utilize magnetic forces to hold a rotary shaft of the turbomachine in a desired position, as opposed to, for example, the forces of a rolling element bearing or oil film bearing. However, failure of the magnetic bearing systems in these turbomachines typically causes the rotary shaft to fall or drop onto an adjacent mechanical surface. Static and dynamic radial and thrust forces acting on the rotary shaft after the failure of the magnetic bearing system may cause substantial damage to the rotary shaft and/or the surrounding components. Accordingly, turbomachine systems often include an auxiliary bearing system configured to “catch” or support the rotary shaft upon failure of the magnetic bearing system to avoid damaging the rotary shaft and/or the surrounding components.
Auxiliary bearing systems may typically be inactive during normal operating conditions when the rotary shaft is supported by the magnetic bearing system. This may be achieved by providing both an axial and radial clearance between interfacing surfaces of the auxiliary bearing system and the rotary shaft. When the magnetic bearing system fails, de-levitation of the rotary shaft occurs and the rotary shaft drops radially onto the auxiliary bearing system. Appropriate portions of the auxiliary bearing system may then compensate for the failed magnetic bearing system by accelerating up to the rotational speed of the rotary shaft. In addition to compensating for the rotational speed of the rotary shaft, the auxiliary bearing system may also provide radial and axial positioning for the rotary shaft. Axial and radial positioning may be provided by axial journals and/or sleeves coupled to the rotary shaft that interface with an inertia ring of the auxiliary bearing system. In positioning the rotary shaft, the axial journals may be subject to extreme accelerations and/or loads from the static and dynamic radial and thrust forces acting on the rotary shaft. Accordingly, repeated failure of the magnetic bearing system to levitate the shaft often results in the wearing and eventual damage of the axial journals, thereby limiting the life of the auxiliary bearing system.
In view of the foregoing, replacement of one or more damaged axial journals in an auxiliary bearing system is often carried out during the operational life of the turbomachine. Typically, axial journals may be coupled to the rotary shaft via an interference fit (e.g., shrink fit). The interference fit used to couple the axial journals, however, may require special tooling (e.g., oven or induction heater) for the removal and replacement of the axial journals, thereby increasing cost and time for replacement thereof.
What is needed, then, is an improved auxiliary bearing system and method of assembly thereof, including a facile and easily replaceable axial journal capable of supporting radial loads while maintaining concentricity or alignment of the rotary shaft.